1. Field of the Invention
Embodiments of the invention relate to a fluidized bed drying apparatus, and more particularly, to a fluidized bed drying apparatus in which target-particles containing moisture, such as brown coal, are exposed to gases having different temperatures and different flow velocities in specified areas of a drying segment to improve drying efficiency.
2. Description for the Related Art
Generally, a fluidized bed drying apparatus has been used for drying efficiently wet particles such as coal, brown coal, slag and limestone, etc., through contact with heated-air over a large area of the particles when the particles are in a state of floating in an upper section of a bed by upward heated-air flow supplied from a lower section of the bed. That is, particles in fluid-like state are floated over a bed of heated-air (or gas) such that the target-particles being dried are well contacted with the heated-air. The drying procedure heat transfer coefficient between the target-particles being dried and the heated-gas is large so that the target-particles are dried rapidly and evenly.
According to prior art fluidized bed drying apparatus, target-particles for being dried are fluidized only in one drying space or floated over one bed using a gas having one set temperature and one set velocity. Typically, the one set temperature and one set flow velocity of the gas for the large amount of heated air needed for the entire prior art fluidized bed drying apparatus is determined based upon what is presumed to be the biggest and wettest particle that will need to be dried. As a result, a large amount of heated air needs to be used to ensure gas-solid contact of the target-particles for being dried is sufficient enough for drying and that the particles fluid flow is sufficiently consistent for even drying of all the particles. Accordingly, a large amount of energy is wasted in the drying of the smaller and/or dryer particles.